Japanese Patent Application Laid-Open Publication No. 2002-208807 and Japanese Patent Application Laid-Open Publication No. 2000-216605 disclose an example of a line transducer (a line transition element) that performs conversion between a microstrip line and a waveguide. FIG. 24 shows a first embodiment, and FIG. 25 shows a second embodiment, of Japanese Patent Application Laid-Open Publication No. 2002-208807. In this conventional technology, a microstrip line 210 and an external waveguide 212 are connected via a dielectric ridged waveguide 211. The line transducer in FIG. 24 includes a multilayer dielectric substrate 201b laminated on an external waveguide 212, a dielectric substrate 201a laminated above this, a ground conductor pattern 202 laminated on the undersurface of the dielectric substrate 201a, a strip conductor pattern 203 laminated on the top surface of the dielectric substrate 201a, waveguide-forming conductor patterns 204a, 204b provided on each surface of the multilayer conductor substrate 201b, ridge-forming conductor patterns 205a, 205b, aground conductor pattern gap 206 provided on the ground conductor pattern 202, a conductor pattern gap 207 provided on the waveguide-forming conductor pattern 204b, and, a waveguide-forming via 208 and a ridge-forming via 209. The strip conductor pattern 203 and ground conductor pattern 202 disposed on the top and bottom of the dielectric substrate 201a form the microstrip line 210. The dielectric substrate 201a, multilayer dielectric substrate 201b, ground conductor pattern 202, waveguide-forming conductor patterns 204a, 204b, ridge-forming conductor patterns 205a, 205b, and waveguide-forming via 208 and ridge-forming via 209, form the dielectric ridged waveguide 211.
The line transducer of FIG. 25 includes ridge-forming vias 209a, 209b, these ridge-forming vias 209a, 209b forming the dielectric ridged waveguide 211, and functioning as a two-step impedance transformer.
In the example disclosed in Japanese Patent Application Laid-Open Publication No. 2000-216605, a line transducer between a microstrip line (radio-frequency line conductor) and the waveguide is a “ridged waveguide” formed in a step-like shape wherein a connecting line conductor is disposed parallel in the same transmission direction as that of the microstrip line, and the gap between upper and lower main conductor layers in the waveguide line of the connecting part is made narrow.